Vernier control devices for use in controlling the direction and amount of movement of a push-pull control cable have been used for many years. Examples of various types of such vernier control devices are disclosed in U.S. Pat. Nos. 3,395,592; 3,405,567; 3,521,502; and 3,643,523, the disclosures of which are included herein by reference.
The control devices described in all of the above described patents, except U.S. Pat. No. 3,521,502, are generally of the type featuring a tubular open-ended sleeve slidably received within an open-ended bore of a housing which itself is characteristically tubular in shape with some type of thread means secured to a wall of the housing bore intermediate the wall and the sleeve. The sleeve is typically able to both rotate and move axially within the housing bore with one end of the sleeve operatively connected to the core of a push-pull cable slidably contained within a casing that is secured to the housing. An operating rod is disposed within a bore of the sleeve and is generally able to move either or both axially and rotationally with respect thereto. The sleeve is generally provided with a single aperture through its wall such that movement of the rod axially or rotationally within the sleeve bore causes a single ball bearing to move radially outwardly through the aperture to the extent necessary to enable a portion of the ball to engage with the threads so that rotation of the sleeve in opposite directions causes the sleeve to move along the housing bore and move the cable core corresponding in opposite axial directions within the cable casing in vernier or incremental amounts and rotational or axial movement of the operating rod into a position other than the thread engagement position causes the ball to move radially inwardly through the aperture an amount sufficient to cause the ball to disengage from the threads and enable the sleeve to be moved axially in opposite directions within the housing bore and move the cable core axially in corresponding opposite directions in gross amounts within the cable casing. Generally included, is some type means such as as a spring for biasing the operating rod into the thread engagement position within the sleeve bore.
Rather than using a ball, the device of U.S. Pat. No. 3,521,502 features a sleeve having a threaded outer wall that can be pivoted into threaded engagement with a small gear tooth rack on one side of the housing bore wall.
The prior art vernier control devices whether by use of a single ball or by a single gear tooth rack have the disadvantage of establishing threaded engagement with the housing bore on only one side of the sleeve which, when the sleeve is threadingly engaged with the threads or gear tooth rack in the housing bore, necesarily concentrates any axial force exerted on the sleeve over a small circumferential area of the threads which may lead to premature wear and stripping of the threads.